The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a running tool for an expandable liner hanger and associated methods.
Expandable liner hangers are generally used to secure a liner within a previously set casing or liner string. These types of liner hangers are typically set by expanding the liner hangers radially outward into gripping and sealing contact with the previous casing or liner string. Many such liner hangers are expanded by use of hydraulic pressure to drive an expanding cone or wedge through the liner hanger, but other methods may be used (such as mechanical swaging, explosive expansion, memory metal expansion, swellable material expansion, electromagnetic force-driven expansion, etc.).
The expansion process is typically performed by means of a running tool used to convey the liner hanger and attached liner into a wellbore. The running tool is interconnected between a work string (e.g., a tubular string made up of drill pipe or other segmented or continuous tubular elements) and the liner hanger.
If the liner hanger is expanded using hydraulic pressure, then the running tool is generally used to control the communication of fluid pressure, and flow to and from various portions of the liner hanger expansion mechanism, and between the work string and the liner. The running tool may also be used to control when and how the work string is released from the liner hanger, for example, after expansion of the liner hanger, in emergency situations, or after an unsuccessful setting of the liner hanger.
The running tool is also usually expected to provide for cementing therethrough, in those cases in which the liner is to be cemented in the wellbore. Furthermore, the running tool is preferably capable of transmitting torque from the work string to the liner, for example, to remediate sticking of the liner in the wellbore, enable the liner to be used as a drill string to further drill the wellbore (in which case a drill bit may be connected to an end of the liner), etc.
It will, thus, be appreciated that many functions are performed by an expandable liner hanger running tool. If these functions are to be performed effectively and reliably, then the operation of the running tool should be appropriately tailored to the environment in which it is to be used.
Unfortunately, past running tool designs have fallen short in one or more respects. Some designs, for example, require a ball or other plug to be dropped through the work string at the completion of the cementing operation and prior to expanding the liner hanger. However, at substantial depths and/or in highly deviated wellbores, it may take a very long time for the ball to reach the running tool (during which time the cement is setting), or the ball may not reach the running tool at all.
Other running tool designs use a release mechanism which operates by shearing pins in response to set down weight (compressive force in the work string). If this set down weight is applied prematurely (e.g., if the liner becomes stuck) or not at all (e.g., in a highly deviated wellbore), then the liner hanger may be released prematurely or not at all.
Still other running tool designs use a release mechanism which operates in response to right-hand (clockwise) torque applied to the work string, or are otherwise incapable of transmitting substantial torque from the work string to the liner. These designs do not allow the liner to be used as a drill string, and do not allow right-hand torque to be used in some circumstances to free a stuck liner.
It will, therefore, be appreciated that improvements are needed in the art of expandable liner hanger running tools and associated methods of installing expandable liner hangers. These improvements can include improvements to operational efficiency, convenience of assembly and operation, improved functionality, etc. not discussed above.